Many studies have been reported concerning the influences of various chemical modification methods on the physical and chemical properties of natural fiber/plastic biocomposites. However, the main issue of biocomposites containing cellulose fibers is poor interphase affinity between the hydrophilic fiber and hydrophobic polymer matrix. The vapor-phase reaction technique has many advantages for the construction of fine-structured composites and coatings, arising covalently bonded compatibilizable components from/at solid substrate surfaces, even if small cracks and holes within the solid substrate. To obtain high-performance biocomposites, the development of modification process for natural fillers including biomass fiber with the vapor-phase technique is introduced in detail for many potential applications of suitably surface-modified biocomposites.